In the case of Manny Pacquiao and Juan Manuel Marquez, the fourth time has to be the charm.
Two of boxing's best have engaged in a riveting trilogy, but when the two square off on Dec. 8 in Las Vegas, Pacquiao needs to deliver the knockout blow in this rivalry's fourth installment.
Almost a year ago to the day, Pacquiao and Marquez engaged in a controversial bout for the World Boxing Organization welterweight title that ended with Pacquiao escaping with a narrow victory.
After their first meeting ended in a draw and the second one ended in another close Pacquiao victory, Marquez certainly has an argument that he's a better fighter.
That's why Pacquiao needs to put an end to this once and for all.
While boxing fans worldwide would love to see a rematch against Floyd Mayweather, Pacman needs to take care of business next month in Las Vegas against the always tough Marquez.
Though Marquez has failed to emerge with a victory in three tries against boxing's best fighter, he's more than held his own.
But holding your own doesn't cut it.
If you want to be the best, you have to beat the best, and Marquez simply can't afford to keep this rivalry rolling without that elusive win.
The owner of 54 career wins desperately needs to make that 55 in order to prevent his name from being just another victim on Pacquiao's lengthy list.
So while Marquez trains and schemes to take down the Filipino sensation, Pacquiao needs to enter this fight with the same vigor, heart and focus as if a championship was on the line.
The aging star has always put on solid performances against Marquez, but he needs to be better than that.
He needs to be the best.
There may not be any championship gold on the line, but every punch Pacquiao throws should be thrown like the sake of his legacy is on the line.
December's bout is a chance to stomp on the throat of this rivalry, and there wouldn't be any better way for Pacquiao to prove he's still the best in the sport than with a resounding victory over one of his toughest opponents.
Before moving on to Mayweather, Pacman needs to land the final knockout against Marquez and file this rivalry away in the record books for good.